極厚鋼板の靱性に及ぼす Al と N の影響

概要

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The effect of Al and N on the notch toughness and tensile strength of heavy section pressure vessel steel plates is investigated. Notch toughness of steel A533B (Mn-Mo-Ni), which has mixed microstructure of ferrite and bainite, is drastically changed by the ratio of sol.N/sol.Al. With metallurgical observations, it is revealed that AlN morphology is influenced by the ratio of sol.N/sol.Al through the level of solute Al(C_<Al>). At the heat treatment of heavy section steel plate, AlN shows OSTWALD ripening and its speed depends upon C_<Al>. When Al is added (Al≧0.010%) in steel and sol.N/sol.Al≦0.5, C_<Al> remains low. This prevents AlN ripening, and brings fine austenite grain size and high toughness. On the other hand, when sol.N/sol.Al<0.5, C_<Al> becomes high and this gives poor toughness through coarse AlN precipitates and coarse austenite grain. Therefore, controll of sol.N/sol.Al over 0.5 is favorable to keep high toughness in A533B steel. In steel A387-22 (Cr-Mo) which has full bainitic microstructure, too fine austenite grain brings about poor hardenability, and polygonal ferrite, which brings about both poor strength and toughness, appears in mi crostructure. Then sol.N/sol.Al<0.5 is better to give high hardenability in steel A387-22.
社団法人日本鉄鋼協会の論文
1988-05-01